As already mentioned hereinbefore, the present application relates to new findings to improve a method of thermal energy recuperation or storage, based on a reversible condensation reaction of inorganic oxoacid compounds, in particular of inorganic phosphorus oxoacid compounds and/or its salts, such as for example with the formation polyphosphoric acid as poly inorganic oxoacid compounds (polymer) and described in the foregoing PCT application.
Such reaction basically consists of two steps (see FIG. 1); wherein in a first step (1) the thermal energy of the source is stored by means of a condensation reaction with the formation of poly inorganic oxoacid compounds (polymers) and the release of water; and wherein in a second step (2) the thermal energy is released from said polymer condensation product by means of a hydrolysation reaction through the addition of water and a release of the inorganic oxoacid compounds (monomers).
As experimentally determined, the condensation or polymerization reaction of FIG. 1, e.g. for pure (poly-) phosphoric acid, works with a thermal energy source at temperatures above about 100° C. It would however be desirable to use waste heat, further also called rest heat, at lower temperatures because of the huge amount of waste heat between 80-100° C. and even gigantic potential of waste heat from e.g. cooling towers of nuclear, coal, gas and other power generation plants working with exhausted rest heat of 50-100° C., typically 60-80° C. It has accordingly been an object of the present invention to find new components to be used as a method to improve the aforementioned condensation reaction, i.e. to make it feasible at lower temperatures of waste heat and make the production unit as compact and economical interesting as possible with faster reactions and process steps in order to find a wide acceptance in the market. It has been found that with the aid of catalysts and azeotropes, waste heat levels of temperatures below 100° C. can be used to drive the condensation or polymerization reaction. Alternatively, at these lower temperatures, one can also work with highly concentrated oxo acid compounds like phosphoric acids that are not polymerized or only polymerized in minor degree. In said instance the basis for the reversibility of the energy storage, mainly resides in the solution heat, i.e. heat released from mixing water and up concentrated oxoacid compounds, and only partially or not substantially in the hydrolysation reaction.
Also this concentration reaction basically consists of two steps (see FIG. 2); wherein in a first step (1) the thermal energy of the source is stored by means of a up concentration process and the release or separation of water by e.g. evaporation; and wherein in a second step (2) the thermal energy is released from said polymer condensation product or highly concentrated oxoacid compound by means of releasing exothermic dilution energy through the addition of water. Evidently, within this process of concentration change, a small amount of the thermal energy may still be used in a condensation reaction with the formation of poly inorganic oxoacid compounds (polymers) and the release of water in a minor degree; in the second step this part of the thermal energy will be released in the hydrolysation reaction with an exothermic release of the inorganic oxoacid compounds (monomers).
Consequently, and when performed at waste heat level below 100° C., the method of thermal energy or storage of the present invention is based on the combination of a reversible concentration and condensation reaction of inorganic oxoacid compounds, wherein in a first step (1) the thermal energy of the source is mainly stored by means of a upconcentration process and partially by means of a condensation reaction with the formation of poly inorganic oxoacid compounds (polymers) and the release of water; and wherein in a second step (2) the thermal energy is released from said polymer condensation product or highly concentrated oxoacid compound by means of an exothermic dilution reaction and by means of a hydrolysation reaction of the poly inorganic oxoacid compounds (polymers) through the addition of water and a release of the inorganic oxoacid compounds (monomers)
The new found components further defined hereinbelow, are chosen not only to speed up the aforementioned process steps and reactions, but also to lower the condensation reaction temperature, control corrosion effects, control solubility of the inorganic Oxo acids and or its salts, control fouling, control deposition of salts or other solids, improve energetic efficiency and many more effects needed to run a process much more economically then in the aforementioned PCT application PCT/EP2012/051025, adjusted to customer needs and continuously for several years with high reliability i.e. without many failures, malfunctions, outages, interruptions et cetera of whatever reason.